Image display apparatus and head mounted display

ABSTRACT

An image display apparatus includes: (A) an image forming device; (B) an optical system that converts light emitted from the image forming device into parallel light; (C) an optical device to which the light beams converted into the parallel light by the optical system enter, in which the light beams are guided, and from which the light beams are emitted; and (D) a supporting member that pivotally supports at least the image forming device with respect to the optical device, wherein an assembly of at least the image forming device and the supporting member has the center of gravity at a position apart from the pivoting central axis of the supporting member, and at least the image forming device is pivoted with respect to the optical device by gravity, whereby the image forming device is horizontally held.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation Application of the U.S. patent application Ser.No. 12/805,636, filed Aug. 11, 2010, which claims priority from JapanesePatent Application No. 2009-199568 filed in the Japanese Patent Officeon Aug. 31, 2009, the entire content of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display apparatus used inorder to allow an observer to observe a two-dimensional image formed byan image forming device, and relates to a head mounted display (HMD)having the image display apparatus incorporated therein and including aframe shaped like glasses to be worn on the head of an observer.

2. Description of the Related Art

A virtual-image display apparatus (image display apparatus) in which avirtual-image optical system allows an observer to view, as an enlargedvirtual image, a two-dimensional image formed by an image forming deviceis widely known from JP-A-2006-162767.

As shown in FIG. 1 that is a conceptual view, an image display apparatus100 includes an image forming device 111 having a plurality of pixelsarrayed in a two-dimensional matrix, a collimating optical system 112for collimating light emitted from the pixels of the image formingdevice 111, and an optical device (a light guide means) 120 on which thelight collimated by the collimating optical system 112 is incident. Theincident light is guided and emitted from the optical device. Theoptical device 120 includes a light guide plate 121, a first deflectingmember 130 (e.g., a single-layer light reflective film), and a seconddeflecting member 140 (e.g., a light reflective multilayer film having amultilayer laminated structure). Incident light propagates in the lightguide plate 121 by total reflection and is then emitted from the lightguide plate 121. The first deflecting member 130 reflects the lightincident on the light guide plate 121 so that light incident on thelight guide plate 121 is totally reflected in the light guide plate 121,and the second deflecting member 140 emits the light, which propagatesin the light guide plate 121 by total reflection, from the light guideplate 121. For example, if HMD is formed by such an image displayapparatus 100, the reduction in weight and size of an apparatus can beachieved.

Further, a virtual-image display apparatus (image display apparatus)using a hologram diffraction grating, in which a virtual-image opticalsystem allows an observer to view, as an enlarged virtual image, atwo-dimensional image formed by an image forming device is widely knownfrom JP-A-2007-94175.

As shown in FIGS. 6A and 6B which are conceptual views, an image displayapparatus 300 basically includes an image forming device 111 fordisplaying an image, a collimating optical system 112, and an opticaldevice (a light guide means) 320 on which the light displayed by theimage forming device 111 is incident. Incident light is guided to an eye41 of an observer. Here, the optical device 320 includes a light guideplate 321, and first and second diffraction grating members 330 and 340provided on the light guide plate 321. Each of the first and seconddiffraction grating members 330 and 340 is formed by a reflective volumehologram diffraction grating. Light emitted from pixels in the imageforming device 111 enters the collimating optical system 112, where thelight is converted into parallel light, and the parallel light entersthe light guide plate 321. The parallel light is incident on and isemitted from a first surface 322 of the light guide plate 321. On theother hand, the first and second diffraction grating members 330 and 340are attached to a second surface 323 of the light guide plate 321parallel to the first surface 322 of the light guide plate 321.

A head mounted display that detects an angle at which the head mounteddisplay is tilted from a horizontal level using an attitude sensor, andalways holds a display image horizontally by image processing or acontrol driving device such as a motor is widely known from, forexample, JP-A-2000-312319. By using the head mounted display having sucha mechanism, even if the head of an observer is tilted, it is possiblefor the observer to observe a horizontal image.

SUMMARY OF THE INVENTION

Meanwhile, the technique disclosed in Japanese Unexamined PatentApplication Publication 2000-312319 has need for rotation transmissionmechanisms such as an attitude sensor and a motor, and has problems suchas an increase in weight of the whole head mounted display, an increasein manufacturing cost, and an increase in power consumption. Further,when a display image is horizontally held by rotating the display imageby image processing, since the display image is rotated in suchprocessing, not only an image forming device which has a large displayarea is needed, but characters, etc. are obliquely displayed. Thus, inorder to display beautiful characters, it is necessary to increase theresolution of the image forming device.

Therefore, it is desirable to provide a head mounted display allowing anobserver to observe a horizontally held image even if the head of anobserver wearing the head mounted display is tilted, without causing anincrease in weight, an increase in manufacturing cost, and an increasein power consumption and without rotating a display image by imageprocessing, and an image display apparatus suitable for use with thehead mounted display.

According to an embodiment of the invention, there is provided an imagedisplay apparatus including:

(A) an image forming device;

(B) an optical system that converts light emitted from the image formingdevice into parallel light;

(C) an optical device to which the light beams converted into theparallel light by the optical system enter, in which the light beams areguided, and from which the light beams are emitted; and

(D) a supporting member that pivotally supports at least the imageforming device with respect to the optical device. Here, an assembly ofat least the image forming device and the supporting member has thecenter of gravity at a position apart from the pivoting central axis ofthe supporting member, and at least the image forming device is pivotedwith respect to the optical device by gravity, whereby the image formingdevice is horizontally held.

According to a first embodiment of the invention, there is provided ahead mounted display including (a) a frame shaped like glasses to beworn on the head of an observer, and (b) an image display apparatusattached to the frame, and the image display apparatus is formed by theimage forming device of the embodiment of the invention described above.The head mounted display according to the first embodiment of theinvention may include one image display apparatus (one-eye type) or twoimage display apparatuses (both-eyes type) of the embodiment of theinvention. There is no relative movement between the optical device andthe frame. That is, the optical device is placed at rest with respect tothe frame.

According to a second embodiment of the invention, there is provided ahead mounted display including:

(a) a frame shaped like glasses to be worn on an observer's head, and

(b) an image forming device pivotally attached to the frame by asupporting member. Here, an assembly of the image forming device and thesupporting member has the center of gravity at a position apart from thepivoting central axis of the supporting member, and the image formingdevice is pivoted with respect to the frame by gravity, whereby theimage forming device is horizontally held. The head mounted displayaccording to the second embodiment of the invention may include oneimage display apparatus (one-eye type) or two image display apparatuses(both-eyes type).

In the image display apparatus according to the embodiment of theinvention or in the image display apparatus in the head mounted displayaccording to the first embodiment of the invention, an assembly of atleast the image forming device and the supporting member has the centerof gravity at a position apart from the pivoting central axis of thesupporting member, and at least the image forming device is pivoted withrespect to the optical device by gravity, whereby the image formingdevice is horizontally held. Further, in the head mounted displayaccording to the second embodiment of the invention, an assembly of theimage forming device and the supporting member has the center of gravityat a position apart from the pivoting central axis of the supportingmember, and the image forming device is pivoted with respect to theframe by gravity, whereby the image forming device is horizontally held.Therefore, the observer can observe a horizontally held image withsimple configuration and structure even if the head of an observerwearing the head mounted display is tilted. Further, an increase inweight, an increase in manufacturing cost, and an increase in powerconsumption are not caused, there is also no need for rotating a displayimage by image processing, an image forming device with a large displayarea is unnecessary, and there is also no need for increasing theresolution of the image forming device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of an image display apparatus of Example1.

FIGS. 2A and 2B are views schematically showing the propagation of lightin a light guide plate that forms the image display apparatus of Example1, and conceptual diagrams showing an arrangement state of the lightguide plate, etc.

FIG. 3 is a schematic view when a head mounted display of Example 1 isviewed from above.

FIG. 4 is a schematic view when the head mounted display of Example 1 isviewed from the side.

FIG. 5 is a conceptual diagram of an image display apparatus of Example2.

FIGS. 6A and 6B are conceptual diagrams of an image display apparatus ofExample 3.

FIG. 7 is a conceptual diagram of an image display apparatus of Example4.

FIG. 8 is a conceptual diagram showing an arrangement state of a lightguide plate, etc. that forms an image display apparatus of Example 5.

FIGS. 9A and 9B are views schematically showing the propagation of lightin a light guide plate that forms an image display apparatus of Example6, and conceptual diagrams showing an arrangement state of the lightguide plate, etc.

FIG. 10 is a schematic view when a head mounted display of Example 6 isviewed from the side.

FIGS. 11A and 11B are views schematically showing the propagation oflight in a light guide plate that forms an image display apparatus ofExample 7, and conceptual diagrams showing an arrangement state of thelight guide plate, etc.

FIG. 12 is a schematic view when a head mounted display of Example 8 isviewed from the side.

FIGS. 13A and 13B are views schematically showing that an observer canobserve a horizontally held image, even if the head of an observerwearing the head mounted display of the embodiment is tilted.

FIGS. 14A and 14B are conceptual diagrams showing an arrangement stateof a modification of a light guide plate, etc. that forms the imagedisplay apparatuses, respectively, of Example 1 and Example 5.

FIG. 15 is a schematic view when one form of the head mounted display ofExample 1 is viewed from the side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, although the invention will be described on the basis ofembodiments with reference to the drawings, the invention is not limitedto the embodiments, and various numeric values and materials in theembodiments are illustrative. Description will be given in the followingorder.

1. Overall description relating to image display apparatus according toembodiment of the invention, and head mounted display according to firstand second embodiments of the invention

2. Example 1 (image display apparatus according to embodiment of theinvention, and head mounted display according to first embodiment of theinvention

3. Example 2 (modification of Example 1)

4. Example 3 (another modification of Example 1)

5. Example 4 (still another modification of Example 1)

6. Example 5 (modification of Embodiments 1 to 4)

7. Example 6 (modification of Embodiments 1 to 5)

8. Example 7 (another modification of Example 6)

9. Example 8 (head mounted display according to second embodiment of theinvention, and others).

[Overall Description Relating to Image Display Apparatus According toEmbodiment of the Invention, and Head Mounted Display According to Firstand Second Embodiments of the Invention]

In the image display apparatus according to the embodiment of theinvention, and an image display apparatus in a head mounted displayaccording to the first embodiment of the invention (hereinafter, theseare generically and simply referred to as the “image display apparatusesaccording to the embodiment of the invention”), the image displayapparatuses can be configured so that a supporting member pivotallysupports an image forming device with respect to an optical device andan optical system. In such a configuration, the image displayapparatuses can be embodied so that the supporting member includes afirst cylindrical member, a second cylindrical member, and a pivotingmember that is disposed between the first cylindrical member and thesecond cylindrical member to relatively pivot the first cylindricalmember and the second cylindrical member, the image forming device isarranged in the first cylindrical member, the optical system is arrangedin the second cylindrical member, and the optical device is attached tothe second cylindrical member.

The arrangement of the image forming device in the first cylindricalmember may be performed by attaching the image forming device to theinner surface of the first cylindrical member by an appropriateattaching member or attaching method. Further, the arrangement of theoptical device in the second cylindrical member may be performed byattaching the optical device to the inner surface of the secondcylindrical member by an appropriate attaching member or attachingmethod. Further, the attachment of the second cylindrical member to theoptical device may be performed by attaching the second cylindricalmember to the optical device by an appropriate attaching member orattaching method. The supporting member, more specifically, the secondcylindrical member may be attached to the frame. This attachment mayalso be performed by an appropriate attaching member or attachingmethod. Further, the supporting member, more specifically, the secondcylindrical member may be fixed to the frame (specifically, the templeportion, the front portion, or the rim portion), or may be detachablyattached to the frame (specifically, the temple portion, the frontportion, or the rim portion).

Alternatively, the image display apparatuses according to the embodimentof the invention can be configured so that the supporting memberpivotally supports the image forming device and the optical system withrespect to the optical device. In such a configuration, the imagedisplay apparatuses according to the embodiment of the invention can beembodied so that the supporting member includes a first cylindricalmember, a second cylindrical member, and a pivoting member that isdisposed between the first cylindrical member and the second cylindricalmember to relatively pivot the first cylindrical member and the secondcylindrical member, the image forming device and the optical system arearranged in the first cylindrical member, and the optical device isattached to the second cylindrical member.

The arrangement of the image forming device and the optical system inthe first cylindrical member maybe performed by attaching the imageforming device and the optical system to the inner surface of the firstcylindrical member by an appropriate attaching member or attachingmethod. Further, the attachment of the second cylindrical member to theoptical device may be performed by attaching the second cylindricalmember to the optical device by an appropriate attaching member orattaching method. The supporting member, more specifically, the secondcylindrical member may be attached to the frame. This attachment mayalso be performed by an appropriate attaching member or attachingmethod. Further, the supporting member, more specifically, the secondcylindrical member may be fixed to the frame (specifically, the templeportion, the front portion, or the rim portion), or may be detachablyattached to the frame (specifically, the temple portion, the frontportion, or the rim portion).

In the image display apparatuses according to the embodiment of theinvention, the assembly of at least the image forming device and thesupporting member has the center of gravity at a position apart(eccentric) from the pivoting central axis of the supporting member.Specifically, the image forming device, etc. may be supported by thesupporting member so that the center of gravity of the assembly is notlocated on the pivoting central axis of the supporting member. Further,in the head mounted display according to the second embodiment of theinvention, the image forming device has the center of gravity at aposition apart (eccentric) from the pivoting central axis of thesupporting member. Specifically, the image forming device may besupported by the supporting member so that the center of gravity of theimage forming device is not located on the pivoting central axis of thesupporting member. That is, more specifically, the image displayapparatuses according to the embodiment of the invention can be embodiedso that the center of gravity of the supporting member coincides withthe pivoting central axis of the supporting member, and the center ofgravity of the image forming device is located apart from the pivotingcentral axis of the supporting member, can be embodied so that thecenter of gravity of the image forming device coincides with thepivoting central axis of the supporting member, and the center ofgravity of the supporting member is located apart from the pivotingcentral axis of the supporting member, and can be embodied so that thecenter of gravity of the whole assembly of the image forming device andthe supporting member is located apart from the pivoting central axis ofthe supporting member. Further, the head mounted display according tothe second embodiment of the invention can be specifically embodied sothat the center of gravity of the supporting member coincides with thepivoting central axis of the supporting member, and the center ofgravity of the image forming device is located apart from the pivotingcentral axis of the supporting member, can be embodied so that thecenter of gravity of the image forming device coincides with thepivoting central axis of the supporting member, and the center ofgravity of the supporting member is located apart from the pivotingcentral axis of the supporting member, and can be embodied so that thecenter of gravity of the whole assembly of the image forming device andthe supporting member is located apart from the pivoting central axis ofthe supporting member.

In the image display apparatuses according to the embodiment of theinvention, the first cylindrical member and the second cylindricalmember that form the supporting member may be made of, for example,plastic or metal, and the sizes (diameters and lengths) of the firstcylindrical member and the second cylindrical member may be determinedin consideration of the sizes of the image forming device, the opticalsystem, the optical device, the whole head mounted display, etc. Thefirst cylindrical member and the second cylindrical member may bearranged in a nested shape via the pivoting member. The firstcylindrical member and the second cylindrical member may be arranged sothat the first cylindrical member covers the second cylindrical member,and the first cylindrical member and the second cylindrical member maybe arranged so that the second cylindrical member covers the firstcylindrical member. The pivoting member arranged disposed between thefirst cylindrical member and the second cylindrical member can be formedby, for example, a ball bearing, a thrust bearing, a roller bearing, anda slide bearing.

In the head mounted display according to the second embodiment of theinvention, the supporting member may be formed by the first cylindricalmember and the second cylindrical member that are made of, for example,plastic or metal, and the sizes (diameters and lengths) of the firstcylindrical member and the second cylindrical member may be determinedin consideration of the sizes of the image forming device, the wholehead mounted display, etc. The first cylindrical member and the secondcylindrical member can be relatively pivoted by arranging the pivotingmember between the first cylindrical member and the second cylindricalmember, similarly to the above. The first cylindrical member and thesecond cylindrical member may be arranged in a nested shape via thepivoting member. The first cylindrical member and the second cylindricalmember may be arranged so that the first cylindrical member covers thesecond cylindrical member, and the first cylindrical member and thesecond cylindrical member may be arranged so that the second cylindricalmember covers the first cylindrical member. The image forming device maybe arranged in the first cylindrical member, and the arrangement of theimage forming device in the first cylindrical member may be performed byattaching the image forming device to the inner surface of the firstcylindrical member by an appropriate attaching member or attachingmethod. Further, the image forming device is attached to the frame bythe supporting member so as to be pivotable to the frame. Specifically,the second cylindrical member may be attached to the frame, morespecifically, the attachment to the frame may be performed by attachingthe second cylindrical member to the frame by an appropriate attachingmember or attaching method. The supporting member may be fixed to theframe (more specifically, the temple portion, the front portion, or therim portion), and may be detachably attached to the frame (morespecifically, the temple portion, the front portion, or the rimportion).

In order to suppress excessive relative rotation between the firstcylindrical member and the second cylindrical member, a pivoting membercan include an appropriate pivoting control member (a kind of brake), oran appropriate pivoting control member (a kind of brake) can be arrangedbetween the first cylindrical member and the second cylindrical member.

In the image display apparatuses according to the embodiment of theinvention, a point where a central light beam that is emitted from thecenter of the image forming device and passes through the nodal point ofthe optical system on the side of the image forming device enters theoptical device is defined as an optical device center point. Further, anaxis that passes through the optical device center point, and isparallel to the axis direction of the optical device is defined as anX-axis, and an axis that passes through the optical device center point,and coincides with the normal axis of the optical device is defined as aY-axis.

In the image display apparatuses according to the embodiment of theinvention, the central light beam can be configured to intersect the XYplane at angles (θ) other than 0 degree. Thereby, there is littlelimitation to the attachment angle of the image display apparatus whenthe image display apparatus is attached to the attaching portion of aframe shaped like glasses, and a high degree of freedom in design can beobtained. In this case, it is preferable from the viewpoint of ease ofhandling, setting, and attachment of the image display apparatus thatthe central light beam be included in the YZ plane. Further, the opticalaxis of the optical system can be configured to be included in YZ planeand intersect the XY plane at angles other than 0 degree, or the opticalaxis of the optical system can be configured to be parallel to the YZplane, be parallel to the XY plane, and pass through a position shiftedfrom the center of the image forming device. Assuming that the XY planecoincides with the horizontal plane, the angle θ at which the centrallight beam intersects the XY plane can be an elevation angle. That is,the central light beam impinges on the XY plane toward the XY plane frombelow the XY plane. In this case, it is preferable the XY planeintersects the vertical plane at angles other than 0 degree, and it isalso preferable that the XY plane intersects the vertical plane at anangle θ. In addition, although the maximum value of θ is not limited,the maximum value can be 5 degrees. Here, the horizontal plane is aplane including a line of sight (“a horizontal line of sight of anobserver”) when the observer views a horizontally located object (forexample, a horizontal direction, an object at an infinite distance, ahorizon, or a horizontal line), and including two eyes of the observerwhich is horizontally located. Further, the vertical plane is a planeperpendicular to this horizontal plane. Alternatively, when an observerviews a horizontally located object (for example, a horizontaldirection, an object at an infinite distance, a horizon, or a horizontalline), a depression angle can be formed by the central light beam thatis emitted from the optical device and enter the eyes of the observer.For example, 5 degrees to 45 degrees can be exemplified as thedepression angle with respect to the horizontal plane.

In the image display apparatuses according to the embodiment of theinvention etc., including the preferable configurations and embodimentsdescribed above, the optical device includes:

(a) a light guide plate from which incident light is emitted after thelight propagates in the light guide plate by total reflection;

(b) a first deflecting member that deflects the light incident on thelight guide plate so that the light incident on the light guide plate istotally reflected in the light guide plate; and

(c) a second deflecting member that deflects the light, which propagatesin the light guide plate by total reflection, multiple times so as toemit the light, which propagates in the light guide plate by totalreflection, from the light guide plate.

The term “total reflection” refers to total internal reflection or totalreflection in the light guide plate. This also applies to the following.The central point of the first deflecting mean is equivalent to anoptical device central point.

Here, the first deflecting member can reflect the light incident on thelight guide plate, and the second deflecting member can transmit andreflect the light, which propagates in the light guide plate by totalreflection, multiple times. In this case, the first deflecting membercan function as a reflecting mirror, and the second deflecting membercan function as a semi-transmissive mirror.

In this configuration, the first deflecting member can be formed by, forexample, a light reflective film (a kind of mirror) made of metalincluding an alloy and configured to reflect the light incident on thelight guide plate, or a diffraction grating (e.g., a hologramdiffraction grating film) for diffracting the light incident on thelight guide plate. The second deflecting member can be formed by amultilayer laminated structure in which multiple dielectric laminatedfilms are laminated, a half mirror, a polarizing beam splitter, or ahologram diffraction grating film. Although the first deflecting memberand the second deflecting member are disposed (incorporated) in thelight guide plate, the first deflecting member reflects or diffractsparallel light incident on the light guide plate so that the incidentparallel light is totally reflected in the light guide plate. On theother hand, the second deflecting member reflects or diffracts theparallel light, which propagates in the light guide plate by totalreflection, multiple times, and emits the parallel light from the lightguide plate.

Alternatively, the first deflecting member can diffract the lightincident on the light guide plate, and the second deflecting member candiffract the light, which propagates in the light guide plate by totalreflection, multiple times. In this case, the first deflecting memberand the second deflecting member each can be formed by a diffractiongrating element. Further, the diffraction grating element can be formedby a reflective diffraction grating element or a transmissivediffraction grating element. Alternatively, one of the diffractiongrating elements can be formed by a reflective diffraction gratingelement, and the other diffraction grating element can be formed by atransmissive diffraction grating element. An example of the reflectivediffraction grating element can include a reflective volume hologramdiffraction grating. For convenience, the first deflecting member formedby a reflective volume hologram diffraction grating is sometimesreferred to as a “first diffraction grating member”, and the seconddeflecting member formed by a reflective volume hologram diffractiongrating is sometimes referred to as a “second diffraction gratingmember” for convenience.

When an image display in color is performed by the image displayapparatuses according to the embodiment of the invention, in order todiffract or reflect a P-number of (e.g., three corresponding to red,green, and blue) types of light beams having a P-number of differentwavelength bands (or wavelengths), in the first diffraction gratingmember or the second diffraction grating member, a P-number ofdiffraction grating layers, each formed by a reflective volume hologramdiffraction grating, can be laminated. Each diffraction grating layer isformed with interference fringes corresponding to one wavelength band(or wavelength). Alternatively, in order to diffract or reflect aP-number of types of light beams having a P-number of differentwavelength bands (or wavelengths), the first diffraction grating memberor the second diffraction grating member can be formed by onediffraction grating layer that is provided with a P-number of types ofinterference fringes. Alternatively, for example, the angle of view canbe divided into three parts, and the first diffraction grating member orthe second diffraction grating member can be formed by laminatingdiffraction grating layers corresponding to the parts of the angle ofview. By adopting these structures, it is possible to increase thediffraction efficiency and acceptable diffraction angle and to optimizethe diffraction angle when the light beams having the wavelength bands(or wavelengths) are diffracted or reflected by the first diffractiongrating member or the second diffraction grating member.

An example of the material that forms the first diffraction gratingmember and the second diffraction grating member can include aphotopolymer material. The material and basic structure of the firstdiffraction grating member and the second diffraction grating memberformed by the reflective volume hologram diffraction gratings may be thesame as those of the reflective volume hologram diffraction gratings inthe related art. The reflective volume hologram diffraction gratingrefers to a hologram diffraction grating that diffracts and reflectsonly +1-order diffracted light. Although the diffraction grating memberis formed with interference fringes extending from the inner side to theouter side of the diffraction grating member, a formation method for theinterference fringes may be the same as that adopted in the related art.Specifically, for example, the material that forms the diffractiongrating member (e.g., a photopolymer material) is irradiated with objectlight in a first predetermined direction, and is simultaneouslyirradiated with reference light in a second predetermined direction,whereby interference fringes to be formed by the object light and thereference light may be recorded in the material that forms thediffraction grating member. By appropriately selecting the firstpredetermined direction, the second predetermined direction, and thewavelengths of the object light and the reference light, theinterference fringes can be arranged at a desired pitch with a desiredslant angle on the surfaces of the diffraction grating member. Here, theslant angle of the interference fringes refers to the angle formedbetween the surfaces of the diffraction grating member (or thediffraction grating layer) and the interference fringes. When the firstdiffraction grating member and the second diffraction grating member areformed to have a laminated structure in which a P-number of diffractiongrating layers, each formed by a reflective volume hologram diffractiongrating, are laminated, a P-number of diffraction grating layers areseparately formed, and are then laminated (bonded) with, for example, anultraviolet curing resin adhesive. Alternatively, a P-number ofdiffraction grating layers may be formed by forming one diffractiongrating layer of an adhesive photopolymer material, and then bondinglayers of an adhesive photopolymer material thereon in order.

Alternatively, the image display apparatuses according to the embodimentof the invention can be embodied so that the optical device is formed bya semi-transmissive mirror that the light emitted from the image formingdevice enters and from which the light is emitted toward the eyes of anobserver. The light emitted from the image forming device can enter thesemi-transmissive mirror after propagating in the air, or afterpropagating in a transparent member such as a glass plate or a plasticplate (specifically, a member formed of a material similar to a materialthat forms the light guide plate, that will be described below). Thesemi-transmissive mirror may be attached to the image forming device viathe transparent member or via a member different from the transparentmember.

The image display apparatuses according to the embodiment of theinvention including the preferable embodiments and configurationsdescribed above can be embodied so that the image forming device has aplurality of pixels arrayed in a two-dimensional matrix. Forconvenience, the image forming apparatus having this configuration isreferred to as an image forming device having a first configuration.

In the image forming device having the first structure, for example, theimage forming device can be formed by an image forming device includinga reflective spatial light modulator and a light source, an imageforming device including a transmissive spatial light modulator and alight source, or an image forming device including a light emittingelement such as an organic EL (Electro Luminescent) element, aninorganic EL element, or a light emitting diode (LED). Especially, it ispreferable that the image forming device include a reflective spatiallight modulator and a light source. For example, the spatial lightmodulator can be formed by a light valve, a transmissive or reflectiveliquid crystal display such as an LCOS (Liquid Crystal On Silicon), or adigital micromirror device (DMD), and the light source can be formed bya light emitting element. Further, the reflective spatial lightmodulator can include a liquid crystal display and a polarizing beamsplitter that reflects and guides part of light from the light source tothe liquid crystal display and transmits and guides part of the lightreflected by the liquid crystal display to an optical system. The lightemitting element that forms the light source can include, for example, ared light emitting element, a green light emitting element, a blue lightemitting element, and a white light emitting element, or white light maybe obtained by performing color mixture and luminance equalization forthe red light, green light, and blue light emitted from the red lightemitting element, the green light emitting element, and the blue lightemitting element using light pipes. The light emitting element can beformed by a semiconductor laser element, a solid-state laser, or an LED.The number of pixels may be determined according to the specificationsof the image display apparatus. For example, a concrete number of pixelscan be 320×240, 432×240, 640×480, 1024×768, or 1920×1080. By arrangingthe light source on the downside, the center of gravity of the imageforming device can be located apart from the pivoting central axis ofthe supporting member.

Alternatively, in the image display apparatuses according to theembodiment of the invention including the preferable embodiments andconfigurations described above, the image forming device can include alight source, and a scanning member that scans the parallel lightemitted from the light source. For convenience, the image formingapparatus having this structure is referred to as an image formingdevice having a second configuration.

The light source in the image forming device having the second structurecan include a light emitting element as a light source, morespecifically, a red light emitting element, a green light emittingelement, a blue light emitting element, and a white light emittingelement, or white light may be obtained by performing color mixture andluminance equalization for the red light, green light, and blue lightemitted from the red light emitting element, the green light emittingelement, and the blue light emitting element using light pipes. Thelight emitting element can be formed by a semiconductor laser element, asolid-state laser, or an LED. The number of pixels (virtual pixels) inthe image forming device having the second structure can also determinedaccording to the specifications of the image display apparatus. Forexample, a concrete number of pixels (virtual pixels) is 320×240,432×240, 640×480, 1024×768, or 1920×1080. When an image display in coloris performed, and the light source includes a red light emittingelement, a green light emitting element, and a blue light emittingelement, for example, it is preferable to perform color synthesis usinga crossed prism. The scanning member can be formed by a MEMS (MicroElectro Mechanical system) having a micromirror rotatable in thetwo-dimensional direction, or a galvanometer mirror, which scans lightemitted from the light source horizontally and vertically. By arrangingthe light source on the downside, the center of gravity of the imageforming device can be located apart from the pivoting central axis ofthe supporting member.

In the image forming device having a first configuration or the imageforming device having a second configuration, the light converted into aplurality of parallel light beams by an optical system (an opticalsystem which converts emitted light into parallel light beams: may bereferred to as a “parallel light emitting optical system”, andspecifically, for example, a collimating optical system or a relayoptical system) is caused to enter the light guide plate. The reason whythe light beams are to be parallel light beams is based on the fact thatit is necessary to store the light wave surface information when suchlight beams have entered the light guide plate even after the lightbeams have been emitted from the light guide plate via the firstdeflecting member and the second deflecting member. In order to generatea plurality of parallel light beams, for example, an optical emittingportion of the image forming device may be located at a place (position)corresponding to the focal length of the parallel light emitting opticalsystem. The parallel light emitting optical system functions to convertpositional information of pixels into angular information in the opticalsystem of the optical device. For example, the parallel light emittingoptical system can be formed by an optical system which has a positiveoptical power as a whole and which includes a convex lens, a concavelens, an adjustable surface prism, or a hologram lens alone or acombination of these. A light-shielding member having an opening may bearranged between the parallel light emitting optical system and thelight guide plate so that the light that is not desired is preventedfrom being emitted from the parallel light emitting optical system andentering the light guide plate.

The light guide plate has two parallel surfaces (first and secondsurfaces) extending parallel to the axis (X-axis) of the light guideplate. Assuming that a surface of the light guide plate on which lightis incident is an incident surface and a surface of the light guideplate from which light is emitted is an exit surface, both the incidentsurface and the exit surface may be defined by the first surface, or theincident surface may be defined by the first surface and the exitsurface may be defined by the second surface. For example, the lightguide plate can be formed of a glass material including optical glasssuch as quartz glass or BK7, or a plastic material (e.g., PMMA,polycarbonate resin, acrylic resin, amorphous polypropylene resin, orstyrene resin including AS resin). The light guide plate is not limitedto a flat plate, and may be curved.

The image forming device in the head mounted display according to thesecond embodiment of the invention can include, for example, an imageforming device formed by a transmissive spatial light modulator, and alight source, specifically, a transmissive liquid crystal display. Thenumber of pixels may be determined according to the specifications ofthe image forming device. For example, a concrete number of pixels canbe 320×240, 432×240, 640×480, 1024×768, or 1920×1080.

By the image display apparatus according to the embodiment of theinvention, for example, a head mounted display can be constructed, thereduction in weight and size of an apparatus can be achieved, thediscomfort when the apparatus is mounted can be significantlyalleviated, and the manufacture cost can be cut down.

In the head mounted display according to the first and secondembodiments of the invention including the preferable embodiments andconfigurations described above, the frame can include a front portion tobe arranged at the front of an observer; and two temple portionspivotally attached to opposite ends of the front portion via hinges. Anend cover portion is attached to a tip portion of each temple portion.

In the head mounted display of the embodiment of the invention includingvarious kinds of configurations and embodiments described above a nosepad can be attached. That is, when an observer views the whole headmounted display of the embodiment of the invention, the assembly of theframe and the nose pad has almost the same structure as normaleyeglasses. Further, the rim portion maybe provided or may not beprovided. The material that forms the frame can be the same material asthe materials which form normal eyeglasses, such as metal, an alloy, orplastic, and combinations thereof. The nose pad can also have awell-known configuration and structure.

In the head mounted display of the embodiment of the invention, it isdesirable from the viewpoints of design or ease of mounting that awiring line (a signal line, a power line, etc.) that extends from one ortwo image forming devices extends to the outside from a tip portion ofan end cover portion via a temple portion and the inside of the endcover portion, and is connected to an external circuit (a controlcircuit). Further, the head mounted display can be embodied so that eachimage forming device includes a headphone portion, and a wiring line forthe headphone portion from each image forming device extends to theheadphone portion via the temple portion and the inside of the end coverportion from the tip portion of the end cover portion. The headphoneportion can include, for example, an inner ear type headphone portionand a canal type headphone portion. More specifically, it is preferablethat the wiring line for the headphone portion extends to the headphoneportion from the tip portion of the end cover portion so as to wraparound behind the auricle (external ear).

The head mounted display of the embodiment of the invention can be usedfor, for example, the display of a title of a film; the display ofvarious descriptions of a play, a kabuki, a Noh play, a kyogen, anopera, a concert, a ballet, various theaters, an amusement park, an artmuseum, a tourist resort, a pleasure resort, a sightseeing guide, etc.;the display of various descriptions or symbols, signs, marks, emblems,designs, etc. in the operation, manipulation, maintenance,disassembling, etc. of various apparatuses; the display of variousdescriptions or symbols, signs, marks, emblems, designs, etc. concerningpersons, objects, etc.; and the display of closed captions.

Example 1

Example 1 relates to an image display apparatus according to theembodiment of the invention, and a head mounted display according to thefirst embodiment of the invention. A conceptual diagram of the imagedisplay apparatus of Example 1 is shown in FIG. 1, the propagation oflight in a light guide plate that forms the image display apparatus ofExample 1 is schematically shown in FIG. 2A, and a conceptual diagramshowing an arrangement state of the light guide plate, etc. that formsthe image display apparatus of Example 1 is shown in FIG. 2B. Further, aschematic view when the head mounted display of Example 1 is viewed fromabove is shown in FIG. 3, and a schematic view when the head mounteddisplay is viewed from the side is shown in FIG. 4.

In Example 1 or Embodiments 2 to 7 that will be described below, animage display apparatus 100, 200, 300, or 400 includes:

(A) an image forming device 111 or 211;

(B) an optical system (parallel light emitting optical system) 112 or254 that converts light emitted from the image forming device 111 or 211into parallel light;

(C) an optical device 120 or 320 which the light beams converted intothe parallel light by the optical system 112 or 254 enter, and areguided therein, and emitted therefrom; and

(D) a supporting member 500 or 600 that pivotally supports at least theimage forming device 111 or 211 with respect to the optical device 120or 320.

Further, a head mounted display of Example 1 or Embodiments 2 to 7 thatwill be described below includes:

(a) a frame 10 shaped like glasses to be worn on the head of anobserver, and

(b) the image display apparatus 100, 200, 300, and 400 attached to theframe 10. In addition, although a both-eyes type display including twoimage display apparatuses has specifically been adopted as the headmounted display of the embodiment, a one-eye type display including oneimage display apparatus may be adopted. The image forming device 111 or211 displays a monochromatic image.

In Example 1 or Embodiments 2 to 7 that will be described below, anassembly of at least the image forming device and the supporting member500 or 600 has the center of gravity CG at a position apart from thepivoting central axis AX of the supporting member 500 or 600, and atleast the image forming device 111 or 211 is pivoted with respect to theoptical device 120 or 320 by gravity, whereby the image forming device111 or 211 is horizontally held. In FIGS. 2A, 8, 12, 14A, and 14B, thepivoting central axis AX of the supporting member 500 or 600 is shown bya dotted line, and an axis passing through the center of gravity CG andparallel to the pivoting central axis AX is shown by a one-dot chainline.

In Example 1 or Embodiments 2 to 4 that will be described below, thesupporting member 500 pivotally supports the image forming device 111 or211 with respect to the optical device 120 or 320 and the optical system112 or 254. The supporting member 500 includes a first cylindricalmember 501, a second cylindrical member 502, and a pivoting member 503that is disposed between the first cylindrical member 501 and the secondcylindrical member 502 to relatively pivot the first cylindrical member501 and the second cylindrical member 502. Further, the image formingdevice 111 or 211 is arranged in the first cylindrical member 501, theoptical system 112 or 254 is arranged in the second cylindrical member502, and the optical device 120 or 320 is attached to the secondcylindrical member 502.

The first cylindrical member 501 and the second cylindrical member 502are made of, for example, plastic or metal. The sizes (diameters andlengths) of the first cylindrical member 501 and the second cylindricalmember 502 may be suitably determined in consideration of the sizes ofthe image forming device 111 or 211, the optical system 112 or 254, theoptical device 120 or 320, the whole head mounted display, etc. Thefirst cylindrical member 501 and the second cylindrical member 502 arearranged in a nested shape via the pivoting member 503 formed by a ballbearing.

The arrangement of the image forming device 111 or 211 in the firstcylindrical member 501 may be performed by attaching the image formingdevice 111 or 211 to the inner surface of the first cylindrical member501 by an appropriate attaching member or attaching method.Specifically, the image forming device is attached by the method offitting a housing 113A or 213A that stores the image forming device 111or 211 to the inner surface of the first cylindrical member 501.Further, the arrangement of the optical system 112 or 254 in the secondcylindrical member 502 maybe performed by attaching the optical system112 or 254 to the inner surface of the second cylindrical member 502 byan appropriate attaching member or attaching method. Specifically, theoptical system is attached by the method of fitting a housing 113B or213B that stores the optical system 112 or 254 to the inner surface ofthe second cylindrical member 502. The supporting member 500, morespecifically, the second cylindrical member 502 is attached to the frame10. Concretely, the supporting member 500, more specifically, the secondcylindrical member 502 is fixed to the frame 10 (more specifically, thetemple portion 13). In addition, the supporting member may be detachablyattached to the temple portion 13. There is no relative movement betweenthe optical device 120 or 320 and the frame 10. That is, the opticaldevice 120 or 320 is placed at rest with respect to the frame 10.

In Example 1 or Embodiments 2 to 7 that will be described below, theassembly of at least the image forming device 111 or 211 and thesupporting member 500 or 600 has the center of gravity CG at a positionapart (eccentric) from the pivoting central axis AX of the supportingmember 500 or 600. Specifically, the image forming device 111 or 211,etc. may be supported by the supporting member 500 or 600 so that thecenter of gravity CG of the assembly is not located on the pivotingcentral axis AX of the supporting member 500 or 600.

In Example 1 or Embodiments 2 to 7 that will be described below, thepoint where a central light beam CL that is emitted from the center ofthe image forming device 111 or 211 and passes through the nodal pointof the optical system 112 or 254 on the side of the image forming deviceenters the optical device 120 or 320 is defined as an optical devicecenter point O, an axis that passes through the optical device centerpoint O, and is parallel to the axis direction of the optical device 120or 320 is defined as an X-axis, and an axis that passes through theoptical device center point O, and coincides with the normal axis of theoptical device 120 or 320 is defined as a Y-axis.

In Example 1 or Embodiments 2 to 7 that will be described below, theoptical device 120 or 320 includes:

(a) a light guide plate 121 or 321 from which incident light is emittedafter the light propagates in the light guide plate by total reflection;

(b) a first deflecting member 130 or 330 that deflects the lightincident on the light guide plate 121 or 321 so that the light incidenton the light guide plate 121 or 321 is totally reflected in the lightguide plate 121 or 321; and

(c) a second deflecting member 140 or 340 that deflects the light, whichpropagates in the light guide plate 121 or 321 by total reflection,multiple times so as to emit the light, which propagates in the lightguide plate 121 or 321 by total reflection, from the light guide plate121 or 321. The central point of the first deflecting member 130 or 330is an optical device central point O. The optical device 120 to 320 is asee-through type (semi-transmissive).

Here, in Example 1, the first deflecting member 130 and the seconddeflecting member 140 are disposed in the light guide plate 121. Thefirst deflecting member 130 reflects light incident on the light guideplate 121, and the second deflecting member 140 transmits and reflectsthe light, which propagates in the light guide plate 121 by totalreflection, multiple times. That is, the first deflecting member 130functions as a reflecting mirror, and the second deflecting member 140functions as a semi-transmissive mirror. More specifically, the firstdeflecting member 130 provided in the light guide plate 121 is formed bya light reflective film (a kind of mirror) made of aluminum andconfigured to reflect light incident on the light guide plate 121. Onthe other hand, the second deflecting member 140 provided in the lightguide plate 121 is formed by a multilayer laminated structure in whichmultiple dielectric laminated films are laminated. The dielectriclaminated films include, for example, a TiO₂ film made of a highdielectric constant material and a SiO₂ film made of a low dielectricconstant material. The multilayer laminated structure in which multipledielectric laminated films are laminated is disclosed inJP-T-2005-521099. Although six dielectric laminated films are shown inthe drawing, the number of dielectric laminated films is not limitedthereto. Thin pieces made of the same material as that of the lightguide plate 121 are sandwiched between the dielectric laminated films.The first deflecting member 130 reflects (or diffracts) parallel lightincident on the light guide plate 121 so that the parallel lightincident on the light guide plate 121 is totally reflected in the lightguide plate 121. On the other hand, the second deflecting member 140reflects (or diffracts) the parallel light, which propagates in thelight guide plate 121 by total reflection, multiple times, and emits theparallel light toward the eye 41 of an observer from the light guideplate 121.

An inclined surface where the first deflecting member 130 is to beformed is formed in the light guide plate 121 by cutting out a portion124 of the light guide plate 121 in which the first deflecting member130 is to be provided, a light reflective film is formed on the inclinedsurface by vacuum deposition, and the cut portion 124 of the light guideplate 121 is then bonded to the first deflecting member 130. Further, amultilayer laminated structure, in which multiple layers made of thesame material (e.g., glass) as that of the light guide plate 121 andmultiple dielectric films (for example, formed by vacuum deposition) arelaminated, is formed, an inclined surface is formed by cutting out aportion 125 of the light guide plate 121 where the second deflectingmember 140 is to be formed, the multilayer laminated structure is bondedto the inclined surface, and the outer side of the light guide plate isshaped by, for example, polishing. Thus, the optical device 120 in whichthe first deflecting member 130 and the second deflecting member 140 areprovided in the light guide plate 121 can be obtained.

In Example 1 or Embodiments 2 to 7 that will be described below, thelight guide plate 121 or 321 formed of optical glass or a plasticmaterial has two parallel surfaces (first surface 122 or 322 and secondsurface 123 or 323) extending parallel to a light propagation direction(X-axis) by the total internal reflection of the light guide plate 121or 321. The first surface 122 or 322 and the second surface 123 or 323face each other. Parallel light enters from the first surface 122 or 322serving as a light incident surface, propagates in the light guide plate121 by total reflection, and is then emitted from the first surface 122or 322 serving as a light exit surface. However, the invention is notlimited thereto, and the light incidence surface may be formed by thesecond surface 123 or 323, and the light exit surface may be formed bythe first surface 122 or 322.

In Example 1 or Example 3 that will be described below, the imageforming device 111 is the image forming device having a firstconfiguration, and has a plurality of pixels arrayed in atwo-dimensional matrix. Specifically, the image forming device 111includes a reflective spatial light modulator 150 and a light source 153formed by a light emitting diode for emitting white light. The wholeimage forming device 111 is stored in a housing 113A (shown by a one-dotchain line in FIG. 1), the optical system 112 is stored in a housing113B (shown by a one-dot chain line in FIG. 1), an opening (not shown)is provided in the housing 113B, and light is emitted through theopening from the optical system (parallel light emitting optical systemor collimating optical system) 112. The reflective spatial lightmodulator 150 includes a liquid crystal display (LCD) 151 formed by anLCOS serving as a light valve, and a polarizing beam splitter 152 thatreflects and guides part of light from the light source 153 to theliquid crystal display 151 and transmits and guides part of the lightreflected by the liquid crystal display 151 to the optical system 112.The liquid crystal display 151 includes a plurality of (e.g., 640×480)pixels (liquid crystal cells) arrayed in a two-dimensional matrix. Thepolarizing beam splitter 152 has the same configuration and structure asthose of the related art. Unpolarized light emitted from the lightsource 153 impinges on the polarizing beam splitter 152. P-polarizedlight components pass through the polarizing beam splitter 152, and areemitted to the outside of the system. On the other hand, S-polarizedlight components are reflected by the polarizing beam splitter 152,enter the liquid crystal display 151, are reflected in the liquidcrystal display 151, and are then emitted from the liquid crystaldisplay 151. Here, light emitted from pixels for displaying white, oflight emitted from the liquid crystal display 151, contains manyP-polarized light components, and light emitted from pixels fordisplaying black contains many S-polarized light components. Therefore,P-polarized light components, of the light that is emitted from theliquid crystal display 151 and impinges on the polarizing beam splitter152, pass through the polarizing beam splitter 152, and are guided tothe optical system 112. On the other hand, S-polarized light componentsare reflected by the polarizing beam splitter 152, and return to thelight source 153. The optical system 112 is formed by, for example, aconvex lens. In order to generate parallel light, the image formingdevice 111 (concretely, the liquid crystal display 151) is arranged at aplace (position) corresponding to the focal length of the optical system112. The light source 153 is arranged on the lower side of the liquidcrystal display 151.

The frame 10 is formed by a front portion 11 arranged at the front of anobserver, two temple portions 13 pivotally attached to both ends of thefront portion 11 via hinges 12, and an end cover portion (referred to asa tip cell, an earmuff, and an ear pad) 14 attached to a tip portion ofeach temple portion 13. Further, a nose pad (not shown) is attached tothe frame. The housing 113B or 213B is detachably attached to the templeportion 13 by the attaching member 18. The frame 10 is made of metal orplastic. The supporting member 500 or 600 may be attached in a statewhere the supporting member is fixed to the temple portion 13 by theattaching member 18. The supporting member may be detachably attached tothe temple portion of the frame of eyeglasses that is possessed by anobserver who possesses and wears the eyeglasses by the attaching member18.

A wiring line (a signal line, a power line, etc.) 15 that extends fromone image forming device 111A extends to the outside from the tipportion of the end cover portion 14 via the temple portion 13 and theinside of the end cover portion 14. Each image forming device 111A or111B includes a headphone portion 16, and a wiring line 17 for theheadphone portion that extends from each image forming device 111A or111B extends to the headphone portion 16 via the temple portion 13 andthe inside of the end cover portion 14 from the tip portion of the endcover portion 14. More specifically, the wiring line 17 for theheadphone portion extends to the headphone portion 16 from the tipportion of the end cover portion 14 so as to wrap around behind auricle(external ear). By adopting such a configuration, a neat head mounteddisplay can be formed without giving the impression that the headphoneportion 16 and the wiring line 17 for the headphone portion is randomlyarranged.

In the image display apparatus 100 of Example 1, the assembly of theimage forming device 111 and the supporting member 500 has the center ofgravity CG at a position apart from the pivoting central axis AX of thesupporting member 500, and the image forming device 111 is pivoted withrespect to the optical device 120 by gravity, whereby the image formingdevice 111 is horizontally held. Therefore, the observer can observe ahorizontally held image with simple configuration and structure even ifthe head of an observer wearing the head mounted display is tilted.FIGS. 13A and 13B schematically show that an observer can observe ahorizontally held image, even if the head of an observer wearing thehead mounted display of the embodiment is tilted. Further, an increasein weight, an increase in manufacturing cost, and an increase in powerconsumption are not caused, there is also no need for rotating a displayimage by image processing, an image forming device with a large displayarea is unnecessary, and there is also no need for increasing theresolution of the image forming device.

Example 2

Example 2 is a modification of Example 1. FIG. 5 is a conceptual view ofan image display apparatus 200 in a head mounted display according toExample 2. As shown in FIG. 5, an image forming device 211 in Example 2is formed by an image forming device having a second configuration. Thatis, the image forming device includes a light source 251, and a scanningmember 253 that scans the parallel light emitted from the light source251. More specifically, the image forming device 211 includes:

(a) a light source 251;

(b) a collimating optical system 252 that converts light emitted fromthe light source 251 into parallel light;

(c) a scanning member 253 that scans the parallel light emitted from thecollimating optical system 252; and

(d) a relay optical system 254 that relays and emits the parallel lightscanned by the scanning member 253. The light source 251, thecollimating optical system 252, and the scanning member 253 are storedin a housing 213A (shown by a one-dot chain line in FIG. 5), a parallellight emitting optical system (relay optical system 254) is stored in ahousing 213B (shown by a one-dot chain line in FIG. 5), an opening (notshown) is provided in the housing 213B, and light is emitted from therelay optical system 254 through the opening. The supporting member 500is detachably attached to the temple portion 13 by the attaching member18. The light source 251 is arranged below the collimating opticalsystem 252 and the scanning member 253.

The light source 251 includes a light emitting element for emittingwhite light. The light emitted from the light source 251 enters thecollimating optical system 252 having a positive optical power as awhole, and is emitted as parallel light. The parallel light is reflectedby a total reflection mirror 256, is horizontally and vertically scannedby the scanning member 253 formed by an MEMS that can rotate amicromirror in a two-dimensional direction so as to two-dimensionallyscan the incident parallel light, and is converted into a kind oftwo-dimensional image, whereby virtual pixels (the number of pixels canbe made the same as that of Example 1) are generated. The light from thevirtual pixels passes through the relay optical system (parallel lightemitting optical system) 254 formed by a relay optical system of therelated art, and light beams converted into parallel light enter theoptical device 120.

The light beams converted into the parallel light by the relay opticalsystem 254 enter the optical device 120, and are guided therein, andemitted therefrom. Since the optical device 120 has the sameconfiguration and structure as that of the optical device adopted inExample 1, a detailed description thereof is omitted. Further, since thehead mounted display of Example 2 has substantially the sameconfiguration and structure as those of the head mounted display ofExample 1 except that the image forming device 211 is different, asdescribed above, a detailed description thereof is omitted.

Example 3

Example 3 is also a modification of Example 1. FIG. 6A is a conceptualview of an image display apparatus 300 in a head mounted displayaccording to Example 3. FIG. 6B is an enlarged schematic sectional viewof a part of a reflective volume hologram diffraction grating. InExample 3, an image forming device 110 is formed by an image formingdevice having a first configuration, similarly to Example 1. An opticaldevice 320 has the same basic configuration and structure as those ofthe optical device 120 of Example 1 except in configurations andstructures of a first deflecting member and a second deflecting member.

In Example 3, the first deflecting member and the second deflectingmember are disposed on a surface of the light guide plate 321(concretely, a second surface 323 of the light guide plate 321). Thefirst deflecting member diffracts light incident on the light guideplate 321, and the second deflecting member diffracts the light, whichpropagates in the light guide plate 321 by total reflection, multipletimes. Here, each of the first and second deflecting members is formedby a diffraction grating element, specifically, a reflective diffractiongrating element, and more specifically, a reflective volume hologramdiffraction grating. In the following description, for convenience, thefirst deflecting member formed by a reflective volume hologramdiffraction grating is sometimes referred to as a “first diffractiongrating member 330”, and the second deflecting member formed by areflective volume hologram diffraction grating is sometimes referred toas a “second diffraction grating member 340”.

In Example 3, or Example 4 that will be described below, in each of thefirst diffraction grating member 330 and the second diffraction gratingmember 340, one diffraction grating layer is laminated. Each diffractiongrating layer made of a photopolymer material is formed withinterference fringes corresponding to one wavelength band (orwavelength), and the interference fringes are formed by a method in therelated art. The interference fringes formed on the diffraction gratinglayers (diffraction optical elements) linearly extend at a fixed pitchand parallel to the Z-axis direction. The axis of the first diffractiongrating member 330 and the axis of the second diffraction grating member340 are parallel to the X-axis, and the normal axis is parallel to theY-axis.

FIG. 6B is an enlarged schematic partial sectional view of a reflectivevolume hologram diffraction grating. The reflective volume hologramdiffraction grating is formed with interference fringes having a slantangle φ. Here, the slant angle φ refers to the angle formed between thesurface of the reflective volume hologram diffraction grating and theinterference fringes. The interference fringes are formed to extend fromthe inner side to the outer side of the reflective volume hologramdiffraction grating. The interference fringes satisfy the Braggcondition. Here, the Bragg condition is to satisfy the followingExpression A. In Expression A, m is a positive integer, λ represents thewavelength, d represents the pitch of the grating surface (distancebetween virtual planes including interference fringes in the normaldirection), and Θ represents the supplementary angle of the incidenceangle on the interference fringes. When light enters the diffractiongrating member at an incidence angle φ, the supplementary angle Θ, theslant angle φ, and the incidence angle φ have the relationship given byExpression B:

M·λ=2·d·sin(Θ)  (A)

Θ=90°−(φ+ψ)  (B)

As described above, the first diffraction grating member 330 is disposed(bonded) on the second surface 323 of the light guide plate 321, anddiffracts and reflects parallel light incident on the light guide plate321 from the first surface 322 so that the parallel light incident onthe light guide plate 321 is totally reflected in the light guide plate321. Further, as described above, the second diffraction grating member340 is disposed (bonded) on the second surface 323 of the light guideplate 321, and diffracts and reflects the parallel light, whichpropagates in the light guide plate 321 by total multiple reflection,and emits the parallel light from the light guide plate 321 through thefirst surface 322.

The parallel light also propagates in the light guide plate 321 by totalreflection, and is then emitted. In this case, since the light guideplate 321 is thin and the optical path in the light guide plate 321 islong, the number of total reflections made until the light beams reachthe second diffraction grating member 340 varies according to the angleof view. More specifically, the number of reflections of parallel lightthat are incident at an angle such as to approach the second diffractiongrating member 340, of parallel light incident on the light guide plate321, is smaller than the number of reflections of parallel light thatare incident on the light guide plate 321 at an angle such as to getaway from the second diffraction grating member 340. This is because theparallel light, which is diffracted and reflected by the firstdiffraction grating member 330 and is incident on the light guide plate321 at an angle such as to approach the second diffraction gratingmember 340, forms a smaller angle to the normal angle at the light guideplate 321 when the light propagating in the light guide plate 321impinges on the inner surface of the light guide plate 321, than theparallel light that is incident on the light guide plate 321 at theangle in the opposite direction. The shape of the interference fringesformed in the second diffraction grating member 340 and the shape of theinterference fringes formed in the first diffraction grating member 330are symmetrical with respect to an imaginary plane perpendicular to theaxis of the light guide plate 321.

The light guide plate 321 in Example 4 that will be described below hasthe same configuration and structure as those of the light guide plate321 described above.

Since the head mounted display of Example 3 has substantially the sameconfiguration and structure as those of the head mounted display ofExample 1 except that the optical device 320 is different, as describedabove, a detailed description thereof is omitted.

Example 4

Example 4 is a modification of Example 3. FIG. 7 is a conceptual view ofan image display apparatus in a head mounted display according toExample 4. In an image display apparatus 400 of Example 4, a lightsource 251, a collimating optical system 252, a scanning member 253, aparallel light emitting optical system (a relay optical system 254),etc. have the same configurations and structures (the image formingdevice having a second configuration) as those adopted in Example 2.Further, an optical device 320 in Example 4 has the same configurationand structure as those of the optical device 320 in Example 3. Since thehead mounted display of Example 4 has substantially the sameconfiguration and structure as those of the head mounted display ofExample 1 except the above-described differences, a detailed descriptionthereof is omitted.

Example 5

Example 5 is a modification of Embodiments 1 to 4. In Embodiments 1 to4, the supporting member 600 pivotally supports the image forming device111 or 211 with respect to the optical device 120 or 320 and the opticalsystem 112 or 254. On the other hand, in Example 5, as shown in FIG. 8that is a conceptual diagram showing an arrangement state of the lightguide plate, etc., the supporting member 600 pivotally supports theimage forming device 111 or 211 and the optical system 112 or 254 withrespect to the optical device 120 or 320. The supporting member 600includes a first cylindrical member 601, a second cylindrical member602, and a pivoting member 603 that is disposed between the firstcylindrical member 601 and the second cylindrical member 602 torelatively pivot the first cylindrical member 601 and the secondcylindrical member 602, the image forming device 111 or 211 and theoptical device 112 or 254 are arranged in the first cylindrical member601, and the optical device 120 or 320 is attached to the secondcylindrical member 602.

The arrangement of the image forming device 111 or 211 and the opticalsystem 112 or 254 in the first cylindrical member 601 may be performedby attaching the image forming device 111 or 211 and the optical system112 or 254 to the inner surface of the first cylindrical member 601 byan appropriate attaching member or attaching method. Specifically, theimage forming device and the optical system are attached by the methodof fitting a housing that stores the image forming device 111 or 211 andthe whole optical system 112 or 254 to the inner surface of the firstcylindrical member 601. Specifically, the attachment of the secondcylindrical member 602 to the optical device 120 or 320 may be performedby attaching the second cylindrical member 602 to the optical device byan appropriate attaching member or attaching method. The supportingmember 600, more specifically, the second cylindrical member 602 isattached to the frame 10. This attachment may also be performed by anappropriate attaching member or attaching method. Further, thesupporting member 600, more specifically, the second cylindrical member602 may be fixed to the frame (specifically, the temple portion 13), ormay be detachably attached to the frame 10 (more specifically, thetemple portion 13).

Since the configuration and structure of the image display apparatus andhead mounted display of Example 5 can be made to be the same as theconfiguration and structure of the image display apparatus and headmounted display of Embodiments 1 to 4 except the above-described points,a detailed description thereof is omitted.

Example 6

Example 6 is a modification of Embodiments 1 to 5. The propagation oflight in the light guide plate that forms the image display apparatus ofExample 6 is typically shown in FIG. 9A, an arrangement state of a lightguide plate, etc. that forms the image display apparatus of Example 6 isshown in FIG. 9B as a conceptual diagram, and a schematic view when thehead mounted display of Example 6 is viewed from the side is shown inFIG. 10.

In Embodiments 1 to 5, the image display apparatus 100 or 300 isdesigned so that the central light beam CL that is emitted from thecenter of the image forming device 111, and passes through the nodalpoint of the optical system 112 or 254 on the side of the image formingdevice impinges on the light guide plate 121 or 321 perpendicularlythereto. That is, the central light beam CL is designed to enter thelight guide plate 121 or 321 at a zero incidence angle. In this case,the center of an image to be displayed coincides with a perpendiculardirection of the first surface 122 or 322 of the light guide plate 121or 321.

In such an image display apparatus represented by the image displayapparatus 100, as shown in FIGS. 2A and 2B, the central light beam CLemitted from the center of the image forming device 111 on the opticalaxis of the collimating optical system 112 is converted intosubstantially parallel light by the collimating optical system 112, andthen enters the first surface (incident surface) 122 of the light guideplate 121 perpendicularly thereto. Then, the light travels along apropagation direction Awhile being totally reflected between the firstsurface 122 and the second surface 123 by the first deflecting member130. Subsequently, the central light beam CL is reflected and diffractedby the second deflecting member 140, is emitted perpendicularly from thefirst surface 122 of the light guide plate 121, and reaches the eye 41of an observer.

When an observer views a horizontally located object in a see-throughtype head mounted display, in order to prevent the optical device 120 or320 from becoming an obstacle, it is necessary to shift and arrange theoptical device 120 or 320 to below a horizontal line of sight of theobserver. In such a case, the whole image display apparatus 100 or 300is arranged below the line of sight of the observer. Meanwhile, in sucha configuration, as shown in FIG. 15, it is necessary to tilt the wholeimage display apparatus 100 by an angle θ″. In this case, the angle θ″by which the image display apparatus 100 can be tilted may be limited orthe degree of freedom in design may become low, from the relationshipwith an attaching portion (a temple portion) of a frame shaped likeglasses for being worn on the head of the observer. Therefore, it ismore desirable to provide an image display apparatus allowing anarrangement with a high degree of freedom and having a high degree offreedom in design so as not to become an obstacle to the horizontal lineof sight of the observer.

In Example 6, the central light beam CL intersects the XY plane at anangle (Θ) other than 0 degree. The central light beam CL is included inthe YZ plane. In Example 6 or Example 7 that will be described below,the optical axis of the optical system 112 or 254 is included in the YZplane, and intersects the XY plane at angles other than 0 degree,specifically, an angle θ (refer to FIGS. 9A and 9B). In the head mounteddisplay of Example 6 or Example 7 that will be described below, assumingthat the XY plane coincides with the horizontal plane, the angle θ atwhich the central light beam CL intersects the XY plane is an elevationangle. That is, the central light beam CL impinges on the XY planetoward the XY plane from below the XY plane. The XY plane intersects avertical plane at angles other than 0 degree, specifically, an angle θ.

In Example 6, θ=5 degrees. More specifically, in such a configuration,the central light beam CL (shown by a dotted line in FIG. 10) isincluded in the horizontal plane. The optical device 120 or 320 istilted by the angle θ with respect to the vertical plane. In otherwords, the optical device 120 or 320 is tilted by the degree of an angle(90-θ) with respect to the horizontal plane. Further, a central lightbeam CL′ (shown by a one-dot chain line in FIG. 10) emitted from theoptical device 120 or 320 is tilted by an angle 2θ with respect to thehorizontal plane. That is, when an observer views the horizontaldirection and an object at an infinite distance, the central light beamCL′ that is emitted from the optical device 120 or 320 and enters theeyes of the observer forms a depression angle θ′ (=2θ) (refer to FIG.10). The angle that the central light beam CL′ forms with the normalangle of the optical device 120 or 320 is θ. In FIG. 9A, or FIG. 11Athat will be described below, a point where the central light beam CL′is emitted from the optical device 120 or 320 is represented by O′, andaxes passing through the point O′ and parallel to the X-axis, theY-axis, and the Z-axis are represented by an X′-axis, a Y′-axis, and aZ′-axis. In addition, the central light beam CL emitted from the centerof the image forming device 111 or 211 is not limited to the form inwhich the central light beam is included in the horizontal plane, andcan be embodied so that the central light beam intersects the horizontalplane at desired angles (depression angle) other than 0 degree. Further,when an observer views the horizontal direction and an object at aninfinite distance, it can be embodied so that the central light beam CL′that is emitted from the optical device 120 or 320 and enters the eyesof the observer forms an elevation angle.

In the image display apparatus of Example 6, or the image displayapparatus that forms the head mounted display of Example 6, the centrallight beam intersects the XY plane at an angle (θ) other than 0 degree.Here, when the central light beam CL′ that is emitted from the opticaldevice and enters the eyes of an observer forms the depression angle θ′,the relationship of θ′=2θ is satisfied. On the other hand, in an exampleshown in FIG. 15, it is necessary to tilt the whole image displayapparatus by the angle θ″ when it is intended to obtain the samedepression angle. Here, the relationship between θ″ and θ is θ″=2θ.Eventually, in the example shown in FIG. 15, the optical device shouldbe tilted by 2θ with respect to the vertical plane. On the other hand,in Example 6, the optical device has only to be tilted by θ with respectto the vertical plane, and the image forming device has only to behorizontally held. Therefore, there is little limitation to theattachment angle of the image display apparatus when the image displayapparatus is attached to the attaching portion of a frame shaped likeglasses, and a high degree of freedom in design can be obtained.Further, since the tilt of the optical device with respect to thevertical plane is smaller than that of the example shown in FIG. 15, aphenomenon that outdoor daylight is reflected by the optical device andenters the eyes of an observer hardly occurs. Therefore, ahigher-quality image can be displayed.

Example 7

Example 7 is a modification of Example 6. The propagation of light in alight guide plate that forms the image display apparatus of Example 7 isschematically shown in FIG. 11A, and a conceptual diagram showing anarrangement state of a light guide plate, etc. that forms the imagedisplay apparatus of Example 7 is shown in FIG. 11B. Here, in Example 7,the optical axis of the optical system (the parallel light emittingoptical system or the collimating optical system) 112 is parallel to theYZ plane, is parallel to the XY plane, and passes through a positionshifted from the center of the image forming device 111. By adoptingsuch a configuration, the central light beam CL is included in the YZplane, and intersects the XY plane at an elevation angle θ.

Example 8

Example 8 relates to a head mounted display according to the secondembodiment of the invention. As shown in FIG. 12 that is a schematicview when viewed from the side, the head mounted display of Example 8includes:

(a) a frame shaped like glasses 10 to be worn on the head of anobserver, and

(b) an image forming device 711 pivotally attached to the frame 10 by asupporting member 700,

The assembly of the image forming device 711 and the supporting member700 has the center of gravity CG at a position apart from the pivotingcentral axis AX of the supporting member 700, and the image formingdevice 711 is pivoted with respect to the optical device 10 by gravity,whereby the image forming device 711 is horizontally held. Although twoimage forming devices 711 are provided in Example 8 (both-eyes type), aone-eye type including one image forming device may be adopted. Further,the image forming device 711 is an image forming device formed by atransmissive spatial light modulator that displays a monochrome (white)image, and a light source, specifically, a transmissive liquid crystaldisplay. The number of pixels is the same as that of Example 1.

In the head mounted display of Example 8, the image forming device 711has the center of gravity CG at a position apart (eccentric) from thepivoting central axis AX of the supporting member 700. Specifically, theimage forming device 711 is supported by the supporting member 700 sothat the center of gravity CG of the image forming device 711 is notlocated on the pivoting central axis AX of the supporting member 700.

Even in Example 8, the supporting member 700 is formed by the firstcylindrical member 701 and the second cylindrical member 702 that aremade of, for example, plastic or metal. The sizes (diameters andlengths) of the first cylindrical member 701 and the second cylindricalmember 702 may be suitably determined in consideration of the sizes ofthe image forming device 711, the whole head mounted display, etc. Thepivoting member 703 similar to Example 1 is arranged between the firstcylindrical member 701 and the second cylindrical member 702, and thefirst cylindrical member 701 and the second cylindrical member 702 canbe relatively pivoted. The first cylindrical member 701 and the secondcylindrical member 702 are arranged in a nested shape via the pivotingmember 703. The image forming device 711 may be arranged in the firstcylindrical member 701, and the arrangement of the image forming device711 in the first cylindrical member 701 may be performed by attachingthe image forming device 711 to the inner surface of the firstcylindrical member 701 by an appropriate attaching member or attachingmethod. Specifically, the image forming device is attached by the methodof fitting the housing of the image forming device 711 into the innersurface of the first cylindrical member 701. Further, the image formingdevice 711 is attached to the frame 10 by the supporting member 700 soas to be pivotable to the frame 10. Specifically, the second cylindricalmember 702 may be attached to the frame 10, more specifically, thesecond cylindrical member 702 may be fixed to or detachably attached tothe rim portion, the front portion 11, or the temple portion 13 by anappropriate attaching member or attaching method.

In the head mounted display of Example 8, the assembly of the imageforming device 711 and the supporting member 700 has the center ofgravity CG at a position apart from the pivoting central axis AX of thesupporting member 700, and the image forming device 711 is pivoted withrespect to the optical device 10 by gravity, whereby the image formingdevice 711 is horizontally held. Therefore, the observer can observe ahorizontally held image with simple configuration and structure even ifthe head of an observer wearing the head mounted display is tilted.Further, an increase in weight, an increase in manufacturing cost, andan increase in power consumption are not caused, there is also no needfor rotating a display image by image processing, an image formingdevice with a large display area is unnecessary, and there is also noneed for increasing the resolution of the image forming device.

Although the invention has been described above on the basis of thepreferable embodiments, the invention is not limited to theseembodiments. The configuration and structure of the image displayapparatus, the supporting member, and the head mounted display that havebeen described in the embodiments are merely illustrative, and can besuitably altered. For example, the structure of the first cylindricalmember and the second cylindrical member in the supporting memberdescribed in Example 1 or Example 5 can also be altered as shown inFIGS. 14A and 14B. That is, a structure can adopted in which the portionof the second cylindrical member 502 or 602 that faces an observer isprovided with a bottom plate 504 or 604, a projection portion 505 or 605is provided toward the inside from a central portion of the bottom plate504 or 604, and the first cylindrical member 501 or 601 pivots via thepivoting member 503 or 603 around the projection portion 505 or 605. Iftwo members that form the supporting member are mutually pivotable, theshape of these members may not be cylindrical. Further, a surfacerelief-type hologram (refer to US Patent Application Publication2004/0062505A1) may be arranged in the light guide plate. The opticaldevice 320 of Example 3 or 4 can also be embodied so that thediffraction grating element is formed by a transmissive diffractiongrating element, or any one of the first deflecting member and thesecond deflecting member is formed by a relfective diffraction gratingelement, and the other is formed by a transmissive diffraction gratingelement. Alternatively, a relfective blazed diffraction grating elementcan also be used as the diffraction grating element.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-199568 filedin the Japan Patent Office on Aug. 31, 2009, the entire contents ofwhich is hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An image display apparatus comprising: an imageforming device; an optical system that converts light emitted from theimage forming device into parallel light; an optical device into whichthe light beams converted into the parallel light by the optical systementer, in which the light beams are guided, and from which the lightbeams are emitted; and a supporting member that pivotally supports atleast the image forming device with respect to the optical device,wherein the image forming device is configured to be moved with respectto the optical device by gravity.
 2. The image display apparatusaccording to claim 1, wherein the optical system is fixed relative tothe optical device.
 3. The image display apparatus according to claim 2,wherein the supporting member includes a first member, a second member,and a pivoting member that is configured to facilitate relative rotationof the first member and the second member, the image forming device isfixed with respect to the first member, and the optical system and theoptical device are fixed with respect to the second member.
 4. The imagedisplay apparatus according to claim 3, wherein the first member and thesecond member are annular cylinders, the image forming device isarranged in an inner region of the first member, the optical system isarranged in an inner region of the second member, and the optical deviceis attached to an end of the second member.
 5. The image displayapparatus according to claim 1, wherein the optical system is fixedrelative to the image forming device.
 6. The image display apparatusaccording to claim 5, wherein the supporting member includes a firstmember, a second member, and a pivoting member that is configured tofacilitate relative rotation of the first member and the second member,the image forming device and the optical system are fixed with respectto the first member, and the optical device is fixed with respect to thesecond member.
 7. The image display apparatus according to claim 6,wherein the first member and the second member are annular cylinders,the image forming device and the optical system are arranged in an innerregion of the first member, and the optical device is attached to an endof the second member.
 8. The image display apparatus according to claim1, wherein the light beams travel in a first direction as they enter theoptical device, are propagated through the optical device in a directionperpendicular to the first direction, and are emitted from the opticaldevice in a direction parallel to the first direction by means of halfmirrors.
 9. The image display apparatus according to claim 1, whereinthe light beams travel in a first direction as they enter the opticaldevice, are propagated through the optical device in a directionperpendicular to the first direction, and are emitted from the opticaldevice in a direction parallel to the first direction by means ofhologram diffraction gratings.
 10. The image display apparatus accordingto claim 1, wherein the image forming device includes a light source anda transmissive spatial light modulator.
 11. The image display apparatusaccording to claim 1, wherein the image forming device includes a lightsource and a reflective spatial light modulator.
 12. The image displayapparatus according to claim 1, wherein the image forming deviceincludes an array of light emitting elements.
 13. A head mounted displaycomprising: a frame shaped like glasses and configured to be wearable onthe head of an observer; and an image display apparatus attached to theframe, the image display apparatus including: an image forming device;an optical system that converts light emitted from the image formingdevice into parallel light; an optical device into which the light beamsconverted into the parallel light by the optical system enter, in whichthe light beams are guided, and from which the light beams are emitted;and a supporting member that pivotally supports at least the imageforming device with respect to the optical device, wherein the imageforming device is configured to be moved with respect to the opticaldevice by gravity.
 14. The head mounted display according to claim 13,wherein the optical system is fixed relative to the optical device. 15.The image display apparatus according to claim 14, wherein thesupporting member includes a first member, a second member, and apivoting member that is configured to facilitate relative rotation ofthe first member and the second member, the image forming device isfixed with respect to the first member, and the optical system and theoptical device are fixed with respect to the second member.
 16. Theimage display apparatus according to claim 15, wherein the first memberand the second member are annular cylinders, the image forming device isarranged in an inner region of the first member, the optical system isarranged in an inner region of the second member, and the optical deviceis attached to an end of the second member.
 17. The image displayapparatus according to claim 13, wherein the optical system is fixedrelative to the image forming device.
 18. The image display apparatusaccording to claim 17, wherein the supporting member includes a firstmember, a second member, and a pivoting member that is configured tofacilitate relative rotation of the first member and the second member,the image forming device and the optical system are fixed with respectto the first member, and the optical device is fixed with respect to thesecond member.
 19. The image display apparatus according to claim 18,wherein the first member and the second member are annular cylinders,the image forming device and the optical system are arranged in an innerregion of the first member, and the optical device is attached to an endof the second member.
 20. A head mounted display comprising: a frameshaped like glasses and configured to be wearable on the head of anobserver, and an image forming device pivotally attached to the frame bya supporting member, wherein the image forming device is configured tobe moved respect to the frame by gravity.